1. Field of the Invention
The present invention concerns an apparatus and method for measuring a bending angle of a sheet.
2. Description of Related Art
Press brake machines adapted to bend metal sheets and obtain profiles with appropriate bending angles are known in the prior art.
Said press brake machines may be provided with bending angle measuring systems comprising a processing unit (computer) and one or more sensors; each sensor normally comprises means adapted to project a light pattern and means adapted to record the pattern deformation during the operation of bending the sheet.
EP 1102032 describes a method for measuring the bending angle of a sheet and a device for measuring said bending angle.
The method comprises measuring, on two sides of a member, e.g. the die, a number of distances on a plane which intersects the sheet and the member. Said distances comprise a number of distances between a measuring instrument and various points on the sheet and a number of further distances between the measuring instrument and various points on the member, so as to determine, for each side of the member, a respective profile of the measured distances and, from the profiles of these distances, the respective angles between sheet and member; the bending angle of the sheet is determined as a function of the angles determined between sheet and member.
The measuring device comprises, on two sides of a member, e.g. the die, an instrument for measuring a number of distances from a plane which intersects the sheet and the member. Said distances comprise a number of distances between a measuring instrument and various points on the sheet and a number of further distances between the measuring instrument and various points on the member. The device comprises means adapted to determine, for each side of the member, a respective profile of the measured distances and means for determining, from the profiles of these distances, the respective angles between sheet and member; the bending angle of the sheet is determined as a function of the angles determined between sheet and member.
EP 1204845 describes a process for detecting a bending angle and an apparatus for determining the change in the bending angle of a sheet during the bending operation.
The process comprises a light beam, which is directed towards a side of the workpiece, the angular position of which must be measured, and is constructed as a light plane or light cone, as a light line or path or, in particular, as a symmetric geometric shape which is produced either on the workpiece or on one side thereof. The change in the position of the contact point during the bending operation is detected in an opto-electronic manner, e.g. by means of a video camera, in particular by means of an array video camera, and the angular position of the side of the workpiece is calculated by the changes in the position of the contact point seen by the video camera.
The light line or path, or the symmetry line of the geometric shape, is projected either parallel or essentially parallel to the bending line of the workpiece on the side of the workpiece, and the change in the angle of the side of the workpiece is calculated by the extension of the parallel translation of said line or lines as seen by the video camera.
The apparatus comprises a measuring beam or light source and a receiver, which records the light paths produced on the workpiece by the measuring beam or light source, in particular an array video camera, and a computer which calculates the angular changes resulting from the changes in position of the light path or paths. The measuring beam or light source is arranged or configured so that the produced path forms at least a slightly curved line or a straight line or a geometrically symmetric shape, surface or figure in order to perform the process as shown above. The apparatus is characterized in that the measuring beam or light source is arranged so that the light line or lines or the like, as the light angle contour delimited in a linear manner, or the symmetry line of the geometric shape, is (or are) arranged so as to extend either parallel or essentially parallel to the bending angle.